1. Field of the Invention
The present invention relates to a spin-valve thin-film magnetic element in which electrical resistance changes due to the relationship between the pinned magnetization direction of a pinned magnetic layer and the magnetization direction of a free magnetic layer which is influenced by an external magnetic field, to a method for fabricating the same, and to a thin-film magnetic head provided with the spin-valve thin-film magnetic element. More particularly, the invention relates to a technique applicable to a spin-valve thin-film magnetic element, in which the stability of the element is improved, for example, Barkhausen noise is reduced.
2. Description of the Related Art
A spin-valve thin-film magnetic element is one type of giant magnetoresistive (GMR) element exhibiting a giant magnetoresistance effect, which detects a recorded magnetic field from a recording medium, such as a hard disk.
The spin-valve thin-film magnetic element has a relatively simple structure compared to other GMR elements, and has a high rate of resistance change relative to changes in an external magnetic field, and thus the resistance changes in response to a weak magnetic field.
FIG. 15 is a sectional view of a conventional spin-valve thin-film magnetic element, viewed from a surface (air bearing surface; ABS) facing a recording medium.
The spin-valve thin-film magnetic element shown in FIG. 15 is a so-called xe2x80x9cbottom-typexe2x80x9d single spin-valve thin-film magnetic element in which an underlying layer 106, an antiferromagnetic layer 101, a pinned magnetic layer 102, a nonmagnetic conductive layer 103, a free magnetic layer 104, and a protective layer 107 are formed in that order on a substrate.
For the spin-valve thin-film magnetic element, a magnetic recording medium, such as a hard disk, travels in the Z direction in the drawing, and a fringing magnetic field from the magnetic recording medium is directed in the Y direction.
The conventional spin-valve thin-film magnetic element shown in FIG. 15 includes a laminate 109 in which the underlying layer 106, the antiferromagnetic layer 101, the pinned magnetic layer 102, the nonmagnetic conductive layer 103, the free magnetic layer 104, and the protective layer 107 are deposited in that order on the substrate; bias layers 105 formed on both sides of the laminate 109 with bias underlying layers 110 therebetween; and electrode layers 108 formed on the bias layers 105.
The underlying layer 106 is composed of Ta or the like, and the antiferromagnetic layer 101 is composed of an Nixe2x80x94O alloy, an Fexe2x80x94Mn alloy, an Nixe2x80x94Mn alloy, or the like. The pinned magnetic layer 102 and the free magnetic layer 104 are composed of Co, a Coxe2x80x94Fe alloy, an Fexe2x80x94Ni alloy, or the like, the nonmagnetic conductive layer 103 is composed of Cu or the like, the bias layers 105 are composed of a Coxe2x80x94Pt alloy or the like, the bias underlying layer 110 is composed of Cr or the like, and the electrode layers 108 are composed of Cu or the like.
Since the pinned magnetic layer 102 is formed in contact with the antiferromagnetic layer 101, an exchange coupling magnetic field (exchange anisotropic magnetic field) is produced at the interface between the pinned magnetic layer 102 and the antiferromagnetic layer 101, and the pinned magnetization of the pinned magnetic layer 102 is pinned, for example, in the Y direction in the drawing.
Since the bias layers 105 are magnetized in the X1 direction in the drawing, the variable magnetization of the free magnetic layer 104 is aligned in the X1 direction. Thereby, the variable magnetization of the free magnetic layer 104 and the pinned magnetization of the pinned magnetic layer 102 are perpendicular to each other.
In the spin-valve thin-film magnetic element, a sensing current is applied from the electrode layers 108 formed on the bias layers 105 to the free magnetic layer 104, the nonmagnetic conductive layer 103, and the pinned magnetic layer 102. A magnetic recording medium, such as a hard disk, travels in the Z direction in the drawing, and when a fringing magnetic field from the magnetic recording medium is applied in the Y direction, the magnetization direction of the free magnetic layer 104 is rotated from the X1 direction to the Y direction. Due to the relationship between the varied magnetization direction of the free magnetic layer 104 and the pinned magnetization direction of the pinned magnetic layer 102, the electrical resistance changes, which is referred to as a magnetoresistance (MR) effect, and the fringing magnetic field from the magnetic recording medium is detected by a voltage change based on the change in the electrical resistance.
The central section sandwiched between the electrode layers 108 corresponds to a sensitive region 104a which substantially contributes to reading of the recorded magnetic field from the magnetic recording medium, and exhibits the magnetoresistance effect, and which also defines the detection track width Tw. Both end sections of the free magnetic layer 104 correspond to insensitive regions 104b which do not greatly contribute to reading of the recorded magnetic field from the magnetic recording medium.
FIG. 16 is a sectional view of another conventional spin-valve thin-film magnetic element, viewed from a surface (ABS) facing a recording medium.
The spin-valve thin-film magnetic element shown in FIG. 16 is a so-called xe2x80x9ctop-typexe2x80x9d single spin-valve thin-film magnetic element in which a protective layer 117, an antiferromagnetic layer 111, a pinned magnetic layer 112, a nonmagnetic conductive layer 113, a free magnetic layer 114, and an underlying layer 116 are deposited in a manner similar to that of the bottom-type single spin-valve thin-film magnetic element described above, but in reversed order.
For the spin-valve thin-film magnetic element, a magnetic recording medium, such as a hard disk, travels in the Z direction in the drawing, and a fringing magnetic field from the magnetic recording medium is directed in the Y direction.
As shown in FIG. 16, the free magnetic layer 114 is formed on the underlying layer 116, the nonmagnetic conductive layer 113 is formed on the free magnetic layer 114, the pinned magnetic layer 112 is formed on the nonmagnetic conductive layer 113, and the antiferromagnetic layer 111 is formed on the pinned magnetic layer 112. The protective layer 117 is formed further on the antiferromagnetic layer 111.
Reference numeral 120 represents a bias underlying layer, reference numeral 115 represents a bias layer, reference numeral 118 represents an electrode layer, and reference numeral 119 represents a laminate.
In the spin-valve thin-film magnetic element, the magnetization direction of the pinned magnetic layer 112 is pinned in a direction opposite to the Y direction.
The underlying layer 116 is composed of Ta or the like, the antiferromagnetic layer 111 is composed of an Nixe2x80x94O alloy, an Fexe2x80x94Mn alloy, an Nixe2x80x94Mn alloy, or the like. The pinned magnetic layer 112 and the free magnetic layer 114 are composed of Co, an Coxe2x80x94Fe alloy, an Fexe2x80x94Ni alloy, or the like, the nonmagnetic conductive layer 113 is composed of Cu or the like, the bias layers 115 are composed of a Coxe2x80x94Pt alloy or the like, the bias underlying layers 120 are composed of Cr or the like, and the electrode layers 118 are composed of Cu or the like.
The electrode layers 118 are formed on the bias layers 115, and the central section sandwiched between the electrode layers 118 corresponds to a sensitive region 114a which substantially contributes to reading of the recorded magnetic field from the magnetic recording medium, and exhibits the magnetoresistance effect, and which also defines the detection track width Tw. Both end sections other than the central section sandwiched between the electrode layers correspond to insensitive regions 114b which do not greatly contribute to reading of the recorded magnetic field from the magnetic recording medium.
A sensing current is applied from the electrode layers 118 to the pinned magnetic layer 112, the nonmagnetic conductive layer 113, and the free magnetic layer 114 in the laminate 119 of the spin-valve thin-film magnetic element in a similar manner to that of the element shown in FIG. 15.
A magnetic recording medium, such as a hard disk, travels in the Z direction in the drawing, and when a fringing magnetic field from the magnetic recording medium is applied in the Y direction, the magnetization direction of the free magnetic layer 114 is rotated from the X1 direction to the Y direction. Due to the relationship between the varied magnetization direction of the free magnetic layer 114 and the pinned magnetization direction of the pinned magnetic layer 112, the electrical resistance changes, which is referred to as an MR effect, and the fringing magnetic field from the magnetic recording medium is detected by a voltage change based on the change in the electrical resistance.
As the recording density has been increased in magnetic recording media, attempts have been made to decrease the recording track width and to decrease the distance between the adjacent recording tracks. When track narrowing is performed by decreasing the recording track width, side reading occurs, in which the insensitive regions 104b or 114b read information in the magnetic recording tracks adjacent to the magnetic recording track that is read by the sensitive region, and the side reading causes noise in output signals, resulting in an error.
The bias layer 105 or 115 in FIG. 15 or 16 is magnetized in the X1 direction due to the coercive force (Hc), since the thickness of the bias layer 105 or 115 is small in the vicinity of the laminate 109 or 119, it is difficult to apply a sufficient bias magnetic field to the free magnetic layer 104 or 114 in the X1 direction. Therefore, the magnetization direction of the free magnetic layer 104 or 114 is not easily stabilized in the X1 direction, resulting in Barkhausen noise.
In order to cope with the problems described above, in the spin-valve thin-film magnetic element shown in FIG. 15 or 16, the bias underlying layer 110 or 120 composed of a Cr film having a body-centered cubic (bcc) structure is provided between a substrate which is not shown in the drawing and the bias layer 105 or 115. The bias underlying layer 110 or 120 acts as a buffer film and an alignment film. As the buffer film, the bias underlying layer 110 or 120 functions as a diffusion barrier when the substrate is exposed to high temperatures due to the subsequent insulating resist hardening step (UV cure or hard bake), etc. in the fabrication process of an inductive head (write head), and the magnetic properties of the bias layer 105 or 115 are prevented from being degraded due to thermal diffusion between the bias layer 105 or 115 and the peripheral layers. With respect to the function as the alignment film, Cr constituting the bias underlying layer 110 or 120 has the bcc structure. The Coxe2x80x94Pt alloy constituting the bias layer 105 or 115 has a mixture of a face-centered cubic (fcc) structure and a hexagonal close-packed (hcp) structure, in which the lattice constant is close to that of Cr. Therefore, in the Coxe2x80x94Pt alloy, the fcc structure is not easily formed, and the hcp structure is easily formed. Consequently, the c-axis of the hcp structure grows while being oriented by priority within the boundary between the Coxe2x80x94Pt alloy and Cr.
Since the hcp structure has a larger magnetic anisotropy in the c-axis direction in comparison with the fcc structure, when a magnetic field is applied to the bias layer 105 or 115, the coercive force (Hc) is further increased. Moreover, since the c-axis of the hcp structure is oriented by priority within the boundary between the Coxe2x80x94Pt alloy and Cr, the remanence (Br) is increased, and the remanence ratio S, which is the ratio of the remanence (Br) to the saturation magnetic flux density (Bs), is also increased. Consequently, the bias magnetic field produced by the bias layer 105 or 115 can be increased, and thus the free magnetic layer 104 or 114 is easily aligned in a single-domain state.
The strong bias magnetic field directed in the X1 direction from the bias layer 105 or 115 is applied to the free magnetic layer 104 or 114 and the magnetization of the free magnetic layer 104 or 114 is aligned in a single-domain state in the X1 direction, and thus Barkhausen noise does not easily occur.
A magnetic head provided with such a thin-film magnetic element can detect a minute change in the magnetic intensity, and thus it is possible to improve the accuracy in write/read into and from a recording medium.
Recently, as the recording density is further improved, the track width of a read element must be further decreased. If narrowing of the track proceeds, since the demagnetizing field in the free magnetic layer in a spin-valve laminate is increased, the bias magnetic field from the bias layer is not effectively applied to the free magnetic layer. Consequently, the magnetic domain is insufficiently controlled, resulting in Barkhausen noise. As described above, as the recording density is increased, the demagnetizing field in the track width direction increases, and there is an increased difficulty in controlling the magnetic domain in order to remove Barkhausen noise. Herein, the demagnetizing field is defined as a magnetic field in which the magnetization direction is opposite to the magnetization direction of magnetic charge accumulated in the edges in the magnetization direction of the free magnetic layer which is a ferromagnetic film.
Therefore, in order to improve the recording density, the demagnetizing field must be decreased, and in order to decrease the demagnetizing field, magnetic charge must be prevented from appearing in the edges of the free magnetic layer magnetized in the track width direction. For that purpose, the bias layer having a larger saturation magnetization than that of the free magnetic layer may be used, and the magnetic field of the bias layer may be effectively applied to the free magnetic layer so that the magnetic charge at the edges of the free magnetic layer is effectively removed. However, the saturation magnetization of a metal layer used for the bias layer is generally small. Although it is may be conceived that the saturation magnetization is increased by using a bias layer having a small saturation magnetization and by increasing the thickness of the bias layer, the idea goes against the trend toward miniaturized elements.
It is an object of the present invention to provide a spin-valve thin-film magnetic element in which a high coercive force (Hc) is secured even in a bias layer composed of a material having low saturation magnetization, and the stability in the magnetosensitive region of a free magnetic layer can be secured.
It is another object of the present invention to provide a method for fabricating such a spin-valve thin-film magnetic element having superior stability in the magnetosensitive region of the free magnetic layer.
It is another object of the present invention to provide a thin-film magnetic head using such a spin-valve thin-film magnetic element having superior stability in the magnetosensitive region of the free magnetic layer, in which Barkhausen noise is reduced and stable operation can be achieved.
In order to overcome the problems associated with the conventional spin-valve thin-film magnetic elements, in the present invention, bias underlying layers are composed of Fe or an Fexe2x80x94Co alloy and the thickness of the bias underlying layers is set at 1.6 to 4.3 nm so that the coercive force of bias layers is increased, and thus a bias magnetic field is effectively applied to the free magnetic layer, the occurrence of a demagnetizing field in the free magnetic layer is inhibited, and the magnetosensitive region is stabilized.
In one aspect of the present invention, a spin-valve thin-film magnetic element includes a laminate formed on a substrate, the laminate including at least an antiferromagnetic layer, a pinned magnetic layer in contact with the antiferromagnetic layer, a nonmagnetic conductive layer in contact with the pinned magnetic layer, and a free magnetic layer in contact with the nonmagnetic conductive layer; bias layers formed on both sides in the track-width direction of the laminate; and electrode layers formed on the bias layers. The bias layers are formed on both sides of the laminate and extend over the peripheral sections of the laminate with ferromagnetic bias underlying layers therebetween, the bias underlying layers being composed of Fe or an Fexe2x80x94Co alloy and having a thickness of 1.6 to 4.3 nm.
In another aspect of the present invention, a spin-valve thin-film magnetic element includes a laminate including a nonmagnetic underlying layer in contact with a substrate, a free magnetic layer in contact with the underlying layer, a nonmagnetic conductive layer in contact with the free magnetic layer, a pinned magnetic layer in contact with the nonmagnetic conductive layer, and an antiferromagnetic layer in contact with the pinned magnetic layer; bias layers formed on both sides in the track-width direction of the laminate; and electrode layers formed on the bias layers. The bias layers are formed on both sides of the laminate and extend over the peripheral sections of the laminate with ferromagnetic bias underlying layers therebetween, the bias underlying layers being composed of Fe or an Fexe2x80x94Co alloy and having a thickness of 1.6 to 4.3 nm.
By using Fe or an Fexe2x80x94Co alloy having a high saturation magnetization with the bcc structure as the bias underlying layer, the bias layer composed of a Ptxe2x80x94Co alloy can have a high coercive force (Hc). Moreover, by limiting the thickness of the bias underlying layer composed of Fe or the Fexe2x80x94Co alloy to a predetermined range, the coercive force (Hc) of the bias layer can be maximized.
Consequently, an increase in the demagnetizing field in the track-width direction of the magnetic element is prevented, and the magnetic domain is easily controlled, thus, Barkhausen noise is suppressed, and the stability of the head can be secured.
The structure of the spin-valve thin-film magnetic element of the present invention will now be described.
In one type of layered structure constituting the magnetosensitive region of the spin-valve thin-film magnetic element, a laminate is formed on a substrate, the laminate including an antiferromagnetic layer, a pinned magnetic layer formed in contact with the antiferromagnetic layer, and a free magnetic layer formed on the pinned magnetic layer with a nonmagnetic conductive layer therebetween; bias layers are formed on both sides in the track-width direction of the laminate; and electrode layers are formed on the bias layers. By forming a bottom type laminate in which deposition is performed in the order as described above, the proportion of a sensing current applied to the laminate, without being passed through the antiferromagnetic layer which has a high resistivity, can be improved, and thus side reading can be prevented, and it is possible to cope with higher magnetic recording densities.
In another type of layered structure constituting the magnetosensitive region of the spin-valve thin-film magnetic element, a laminate includes a nonmagnetic underlying layer formed on a substrate, a free magnetic layer formed such that it is in contact with the underlying layer, a pinned magnetic layer formed on the free magnetic layer with a nonmagnetic conductive layer therebetween, and an antiferromagnetic layer formed on the pinned magnetic layer; bias layers are formed on both sides in the track-width direction of the laminate; and electrode layers are formed on the bias layers. By forming a top-type laminate in which deposition is performed in the order described above, it is possible to increase the proportion of the sensing current directly applied to the pinned magnetic layer, the nonmagnetic conductive layer, and the free magnetic layer located below the antiferromagnetic layer through the bias layers.
In the spin-valve thin-film magnetic element of the present invention, the antiferromagnetic layer is preferably composed of a Ptxe2x80x94Mn alloy. Instead of the Ptxe2x80x94Mn alloy, the antiferromagnetic layer may be composed of one of an Xxe2x80x94Mn alloy and a Ptxe2x80x94Mnxe2x80x94Xxe2x80x2 alloy, where X is an element selected from the group consisting of Pd, Ir, Rh, Ru, and Os, and Xxe2x80x2 is at least one element selected from the group consisting of Pd, Cr, Ru, Ni, Ir, Rh, Os, Au, Ag, Ne, Ar, Xe, and Kr. Furthermore, an Nixe2x80x94O alloy, an Fexe2x80x94Mn alloy, an Nixe2x80x94Mn alloy, or the like may be used as the antiferromagnetic layer.
By fabricating the spin-valve thin-film magnetic element in which the antiferromagnetic layer is composed of an Xxe2x80x94Mn alloy or an Xxe2x80x2xe2x80x94Ptxe2x80x94Mn alloy, a larger exchange coupling magnetic field can be applied by the antiferromagnetic layer, and superior characteristics, such as a high blocking temperature and superior corrosion resistance, are exhibited.
In the spin-valve thin-film magnetic element of the present invention, since the pinned magnetic layer is formed in contact with the antiferromagnetic layer, an exchange coupling magnetic field (exchange anisotropic magnetic field) is produced at the interface between the pinned magnetic layer and the antiferromagnetic layer, and the pinned magnetization is pinned in a certain direction.
The pinned magnetic layer is composed of a ferromagnetic material, such as Co, an Nixe2x80x94Fe alloy, a Coxe2x80x94Nixe2x80x94Fe alloy, a Coxe2x80x94Fe alloy, or a Coxe2x80x94Ni alloy, and preferably has a thickness of 2 to 4 nm.
In the spin-valve thin-film magnetic element of the present invention, the nonmagnetic conductive layer is composed of a nonmagnetic metal, such as Cu, Cr, Au, Ag, Rh, or Ir, and usually has a thickness of 2 to 4 nm. The nonmagnetic conductive layer allows spin-dependent scattering of conduction electrons to occur at the interface between the ferromagnetic pinned magnetic layer and the free magnetic layer, resulting in a giant magnetoresistance effect (GMR effect).
In the spin-valve thin-film magnetic element of the present invention, the free magnetic layer is composed of a ferromagnetic material, such as Co, an Nixe2x80x94Fe alloy, a Coxe2x80x94Nixe2x80x94Fe alloy, a Coxe2x80x94Fe alloy, or a Coxe2x80x94Ni alloy, similar to the pinned magnetic layer.
When a fringing magnetic field is applied from a recording medium to the free magnetic layer, the magnetization of the free magnetic layer changes, spin-dependent scattering of conduction electrons occurs at the interface with the nonmagnetic conductive layer and at the interface between the nonmagnetic conductive layer and the pinned magnetic layer, resulting in a change in electrical resistance, and the fringing magnetic field from the recording medium is thereby detected.
As described above, the antiferromagnetic layer, the pinned magnetic layer, the nonmagnetic conductive layer, and the free magnetic layer are disposed on the substrate, and a protective layer composed of a nonmagnetic metal, such as Ta, is provided thereon, and thus a laminate constituting the magnetosensitive region is obtained.
The laminate is then subjected to ion milling or the like, which will be described below, to produce a substantially trapezoidal cross-section. Bias layers are provided on both sides of the trapezoidal laminate, and conductive layers are provided on the bias layers.
The bias layers effectively apply a bias magnetic field to the free magnetic layer so that the demagnetizing field is suppressed in the free magnetic layer and the free magnetic layer is aligned in a single-domain state, and thus Barkhausen noise is suppressed, enabling stable operation of the magnetosensitive region. For that purpose, the bias layers preferably have as large a saturation magnetization as possible.
Preferably, the bias layers are composed of a Coxe2x80x94Pt alloy, a Coxe2x80x94Crxe2x80x94Pt alloy, a Coxe2x80x94Crxe2x80x94Ta alloy, or the like, and have a thickness of approximately 20 to 50 nm.
At least one bias layer is formed on each inclined side of the trapezoidal laminate, and the bias magnetic field is applied from the side of the laminate. The bias layers also extend over the peripheral sections of the laminate.
In the present invention, in order to increase the coercive force of the bias layers and to effectively apply the bias magnetic field to the free magnetic layer, a ferromagnetic material, such as Fe or an Fexe2x80x94Co alloy, is used as the bias underlying layer, instead of the conventionally used Cr, and the thickness thereof is set at 1.6 to 4.3 nm.
The Coxe2x80x94Pt alloy preferably used as the bias layer has a mixture of a face-centered cubic (fcc) structure and a hexagonal close-packed (hcp) structure, which resembles a body-centered cubic (bcc) structure. The Fe or Fexe2x80x94Co alloy used as the bias underlying layer has a body-centered cubic (bcc) structure, and the lattice constant thereof is close to that of the Coxe2x80x94Pt alloy. The Fe or Fexe2x80x94Co alloy has a higher saturation magnetization than that of the Coxe2x80x94Pt alloy used as the bias layer. Therefore, by depositing the Coxe2x80x94Pt alloy using the Fe or the Fexe2x80x94Co alloy as the bias underlying layer, the coercive force of the bias layer can be increased. Incidentally, example values of the coercive force Hc (Oe) and the saturation magnetization Ms (emu/cc) in Fexe2x80x94Co alloys having different Co contents are Hc=30 Oe and Ms=1,875 emu/cc in Fe50xe2x80x94Co50 alloy, Hc=19 Oe and Ms=1,600 emu/cc in Fe85xe2x80x94Co15 alloy, and Hc=20 Oe and Ms=1,425 emu/cc in Fe95xe2x80x94Co5 alloy.
It has been found that when the thickness of the Fe or Fexe2x80x94Co alloy as the bias underlying layer is 2.0 nm, the coercive force of the Coxe2x80x94Pt alloy as the bias layer is at a maximum. FIG. 1 is a graph showing the relationship between the coercive force of the Coxe2x80x94Pt alloy and the thickness of the Fexe2x80x94Co alloy underlying film. FIG. 1 shows the change in the coercive force (Hc) as the Coxe2x80x94Pt alloy is deposited in the direction of the Fexe2x80x94Co alloy orientation. The coercive force of the Fexe2x80x94Co/Coxe2x80x94Pt alloy laminate rapidly increases as the thickness of the Fexe2x80x94Co alloy film approaches 1.0 nm, and reaches its highest value, exceeding 1,000 Oe, when the thickness of the Fexe2x80x94Co alloy film is 2.0 nm. After that, as the thickness of the Fexe2x80x94Co alloy film is increased, the coercive force gradually decreases.
Since the most desirable value of the coercive force of the bias layer is 750 Oe or more, the preferred thickness of the bias underlying layer is 1.6 to 4.3 nm. As shown in FIG. 1, when the thickness of the Fexe2x80x94Co alloy is less than 2.0 nm, the coercive force of the Fexe2x80x94Co/Coxe2x80x94Pt alloy laminate rapidly decreases with thickness, and therefore, when the Fexe2x80x94Co alloy bias underlying layer is formed, the thickness must be controlled so as not to greatly fall below 2.0 nm. For example, if the thickness of the Fexe2x80x94Co alloy bias underlying layer is set at 1.7 to 3.5 nm, it is possible to maintain the coercive force of the Fexe2x80x94Co/Coxe2x80x94Pt alloy laminate bias layer above 750 Oe, and if the thickness of the Fexe2x80x94Co alloy bias underlying layer is set at 1.8 to 2.5 nm, it is possible to maintain the coercive force of the Fexe2x80x94Co/Coxe2x80x94Pt alloy laminate bias layer above 850 Oe.
As described above, the coercive force of the Fexe2x80x94Co/Coxe2x80x94Pt laminate bias layer changes significantly with thickness being greatest when the thickness of the Fexe2x80x94Co alloy bias underlying layer is 2.0 nm. Moreover, when the thickness of the Fexe2x80x94Co alloy bias underlying layer is decreased below 2.0 nm, the coercive force rapidly decreases. In order to effectively apply the bias magnetic field to the free magnetic layer, the thickness of the bias underlying layers, which are adjacent to the free magnetic layer, on both sides in the track-width direction of the laminate is preferably more than or equal to the thickness of the bias underlying layers extending over the peripheral sections other than the both sides in the track-width direction of the laminate. Since most of the bias underlying layers extend over the peripheral sections of the laminate, it is also important to increase the coercive force of the bias underlying layers extending over the peripheral sections of the laminate. Therefore, the thickness of the bias underlying layers is set so that the thickness of the bias underlying layers on both sides in the track-width direction of the laminate is larger than or equal to the thickness of the bias layers extending over the peripheral sections of the laminate, within the range of 1.6 to 4.3 nm.
The bias underlying layers in which the thickness is thus controlled may be formed, for example, by any one of ion-beam sputtering, long-throw sputtering, and collimation sputtering, or by a method in which these are combined, which will be described in detail below.
The conductive layers disposed on the bias layers apply a sensing current to the free magnetic layer, the nonmagnetic conductive layer, and the pinned magnetic layer. The conductive layers are composed of a highly conductive metal, such as Cr, Ta, or Au.
In the present invention, the pinned magnetic layer may include a first pinned magnetic sublayer in which the magnetization direction is pinned due to an exchange anisotropic magnetic field with the antiferromagnetic layer, and a second pinned magnetic sublayer formed on the first pinned magnetic sublayer with a nonmagnetic intermediate layer therebetween, the magnetization direction of the second pinned magnetic sublayer being aligned antiparallel to the magnetization direction of the first pinned magnetic sublayer.
In the spin-valve thin-film magnetic element, the first pinned magnetic sublayer is provided on the antiferromagnetic layer side of the nonmagnetic intermediate layer, and the second pinned magnetic sublayer is provided on the nonmagnetic conductive layer side of the nonmagnetic intermediate layer.
The first pinned magnetic sublayer and the second pinned magnetic sublayer are composed of a ferromagnetic material, such as Co, an Nixe2x80x94Fe alloy, or an Fexe2x80x94Co alloy. The nonmagnetic intermediate layer is composed of a nonmagnetic material, such as Ru.
At the interface between the first pinned magnetic sublayer and the antiferromagnetic layer, an exchange coupling magnetic field (exchange anisotropic magnetic field) is produced and the magnetization of the first pinned magnetic sublayer is pinned in a certain direction. The second pinned magnetic sublayer is antiferromagnetically coupled to the first pinned magnetic sublayer, and the magnetization of the second pinned magnetic sublayer is pinned in a direction opposite to that of the first pinned magnetic sublayer.
Since the magnetization directions of the first pinned magnetic sublayer and the second pinned magnetic sublayer are antiparallel to each other, the magnetic moments of the first pinned magnetic sublayer and the second pinned magnetic sublayer cancel out each other. However, when the thickness of the first pinned magnetic sublayer is larger than the thickness of the second pinned magnetic sublayer, the spontaneous magnetization resulting from the first pinned magnetic sublayer slightly remains, and thus the pinned magnetic layer is in a ferrimagnetic state. The exchange coupling magnetic field with the antiferromagnetic layer is further amplified by the apparent spontaneous magnetization, and the magnetization of the pinned magnetic layer is pinned.
In the present invention, preferably, the laminate further includes a nonmagnetic underlying layer deposited as an undermost layer and a nonmagnetic protective layer deposited as an uppermost layer, and the free magnetic layer may include a first free magnetic sublayer and a second free magnetic sublayer separated by a nonmagnetic intermediate layer, the first free magnetic sublayer being disposed on the nonmagnetic protective layer or the nonmagnetic underlying layer side, and the second free magnetic sublayer being disposed on the nonmagnetic conductive layer side.
In the free magnetic layer of the spin-valve thin-film magnetic element, for example, the first free magnetic sublayer is provided on the protective layer side of the nonmagnetic intermediate layer, and the second free magnetic sublayer is provided on the nonmagnetic conductive layer side of the nonmagnetic intermediate layer.
The first free magnetic sublayer and the second free magnetic sublayer are composed of a ferromagnetic material, such as an Nixe2x80x94Fe alloy, and the nonmagnetic intermediate layer is composed of a nonmagnetic material, such as Ru.
The thickness t1 of the first free magnetic sublayer is set smaller than the thickness t2 of the second free magnetic sublayer.
When the saturation magnetization of the first free magnetic sublayer and the saturation magnetization of the second free magnetic sublayer are set at M1 and M2, respectively, the magnetic thickness of the first free magnetic sublayer and the magnetic thickness of the second free magnetic sublayer are M1xc2x7t1 and M2xc2x7t2, respectively, and the magnetic thicknesses of the first free magnetic sublayer and the second free magnetic sublayer are set so as to satisfy the relationship, M2xc2x7t2 greater than M1xc2x7t1. The first free magnetic sublayer and the second free magnetic sublayer are antiferromagnetically couplable to each other. That is, when the magnetization direction of the first free magnetic sublayer is determined by the bias layer, the magnetization direction of the second free magnetic sublayer is aligned in a direction opposite to the magnetization direction of the first free magnetic layer. Since the relationship M2xc2x7t2 greater than M1xc2x7t1 is satisfied, the magnetization of the second free magnetic sublayer remains, and the magnetization direction of the entire free magnetic layer is aligned in the magnetization direction of the sublayer having a larger magnetic thickness. At this stage, the effective magnetic thickness of the free magnetic layer is expressed as (M2xc2x7t2xe2x88x92M1xc2x7t1).
As described above, the first free magnetic sublayer and the second free magnetic sublayer are antiferromagnetically coupled to each other so that the magnetization directions are antiparallel to each other, and the magnetic thicknesses of the two sublayers satisfy the relationship M2xc2x7t2 greater than M1xc2x7T1, and thus a synthetic ferrimagnetic state is formed. Consequently, the magnetization direction of the free magnetic layer and the magnetization direction of the pinned magnetic layer are perpendicular to each other.
In the spin-valve thin-film magnetic element, when the magnetization direction of the free magnetic layer changes due to a fringing magnetic field from a recording medium, such as a hard disk, the electrical resistance changes due to the relationship with the magnetization of the pinned magnetic layer, and the fringing magnetic field from the recording medium is detected by voltage change caused by the change in the electrical resistance.
Since the free magnetic layer includes the first and second free magnetic sublayers antiferromagnetically coupled to each other, the magnetization direction of the entire free magnetic layer is varied by a small external magnetic field, and thus the sensitivity of the spin-valve thin-film magnetic element is improved.
If the spin-valve thin-film magnetic element of the present invention as described above is used for a magnetic head, the bias magnetic field is effectively applied to the free magnetic layer, an increase of the demagnetizing field in the free magnetic layer of the spin-valve laminate is inhibited, and the magnetic charge in the edges of the free magnetic layer can be effectively removed, and thus the free magnetic layer is completely aligned in a single-domain state. Consequently, it is possible to provide a thin-film magnetic head, which is suitable for track narrowing of the read element which is associated with further improvement in recording density, and in which Barkhausen noise is reduced and stable operation can be achieved.
In another aspect of the present invention, a method for fabricating a spin-valve thin-film magnetic element includes the steps of:
forming a laminate by depositing, at least, an antiferromagnetic layer, a pinned magnetic layer in contact with the antiferromagnetic layer, a nonmagnetic conductive layer in contact with the pinned magnetic layer, and a free magnetic layer in contact with the nonmagnetic conductive layer in that order on a substrate;
forming a lift-off resist layer on the laminate;
removing the region which is not covered with the lift-off resist layer by ion milling so that the laminate has a trapezoidal cross-section;
forming bias underlying layers by performing sputtering on both inclined sides of the laminate and over the peripheral sections of the laminate while a sputtering target comprising Fe or an Fexe2x80x94Co alloy is opposed to the substrate at a predetermined angle so that the thickness of the bias underlying layers on the inclined sides of the laminate is equal to or larger than the thickness of the bias underlying layers over the peripheral sections of the laminate;
forming bias layers on the bias underlying layers by sputtering; and
forming electrode layers on the bias layers by sputtering.
Alternatively, the laminate is formed by depositing, at least, a free magnetic layer, a nonmagnetic conductive layer in contact with the free magnetic layer, a pinned magnetic layer in contact with the nonmagnetic conductive layer, and an antiferromagnetic layer in contact with the pinned magnetic layer in that order on a substrate.
In the method for fabricating the spin-valve thin-film magnetic element of the present invention, in the step of forming the laminate, a so-called synthetic-ferri-pinned type pinned magnetic layer may be formed, which pinned magnetic layer including a first pinned magnetic sublayer and a second pinned magnetic sublayer formed on the first pinned magnetic sublayer with a nonmagnetic intermediate layer therebetween.
In the method for fabricating the spin-valve thin-film magnetic element of the present invention, in the step of forming the laminate, a so-called synthetic-ferri-free type free magnetic layer may be formed, which free magnetic layer including a first free magnetic sublayer and a second free magnetic sublayer separated by a nonmagnetic intermediate layer, the first free magnetic sublayer being disposed on the nonmagnetic protective layer or nonmagnetic underlying layer side, and the second free magnetic sublayer being disposed on the nonmagnetic conductive layer side.
In the step of forming the laminate, the individual layers are deposited on the substrate or an underlying layer provided on the substrate by sputtering to achieve predetermined thicknesses.
Next, on the surface of the laminate thus formed, a lift-off resist pattern with a predetermined size is formed. After the laminate has been provided with the resist pattern, a portion other than the shadow portion of the resist pattern is removed by etching, such as ion milling, and a substantially trapezoidal laminate is obtained.
Next, the bias underlying layers are formed by any one of ion-beam sputtering, long-throw sputtering, and collimation sputtering, or by a method in which these are combined. In the present invention, it is important to accurately control the thicknesses of the bias underlying layers composed of Fe or the Fexe2x80x94Co alloy. In view of this, preferably, any one of ion-beam sputtering, long-throw sputtering, and collimation sputtering in which the irradiation direction of sputtered particles can be limited to a narrow range is used. When such a sputtering method is carried out, a sputtering target composed of Fe or the Fexe2x80x94Co alloy for forming the bias underlying layers is positioned at an angle to the substrate provided with the trapezoidal laminate, the angle is appropriately set, and sputtered particles are accurately deposited on the intended section, and thus the bias underlying layers with desired thicknesses can be obtained. Moreover, it is also possible to make the thickness of the bias underlying layers on the sides in the track-width direction of the laminate larger than the thickness of the bias underlying layers extending over the peripheries of the laminate.
When the bias underlying layers are deposited, preferably, the substrate is rotated so that the bias underlying layers are uniformly deposited.
By appropriately setting the angle of incidence of sputtered particles to the substrate, namely, the deposition angle (xcex8), it is possible to control the thickness of the bias underlying layers accurately and at a predetermined thickness. Therefore, the setting of the deposition angle (xcex8) is important.
Usually, the angle (xcex1) between the substrate and the inclined surface of the laminate is approximately 15 to 60 degrees, and preferably 20 to 50 degrees.
When the angle (xcex1) between the substrate and the inclined surface of the laminate was changed from 20 to 60 degrees in order to set the thickness (b) of the bias underlying layer formed on the inclined surface of the laminate at 2.0 nm, the ratio (b/a) of the thickness (b) of the bias underlying layer formed on the inclined surface of the laminate to the thickness (a) of the bias underlying layer extending over the peripheral sections of the laminate was examined. FIG. 2 is a graph showing the results thereof.
As is obvious from FIG. 2, it is when the deposition angle (xcex8) is 7 degrees or more the ratio b/a is equal to 1 while both the thickness (a) of the bias underlying layer extending from the bottom of the inclined surface of the laminate, parallel to the substrate, and the thickness (b) of the bias underlying layer formed on the inclined surface are 2.0 nm.
As described above, when the thickness of the bias underlying layer is below 2.0 nm, the coercive force of the bias layer rapidly decreases, and this is not desirable. Therefore, preferably, both the thickness (a) of the bias underlying layer extending over the peripheries of the laminate and the thickness (b) of the bias underlying layer formed on the inclined surface of the laminate are more than 2.0 nm and are infinitesimally close to 2.0 nm. At this stage, the ratio b/a is preferably greater than 1 and is infinitesimally close to 1.
In view of the coercive force of the bias layer, the permissible thicknesses (a) and (b) of the bias underlying layers are approximately 1.6 to 4.6 nm, and the thickness (b) is desirably 2.0 nm, and therefore, the upper limit of the ratio b/a is 2.15. Most preferably, both the thickness (a) and the thickness (b) are 2.0 nm and the ratio b/a is 1. Consequently, it is apparent from FIG. 2 that in order to obtain a ratio b/a of 1.0 to 2.15, the deposition angle (xcex8) must be 19 to 70 degrees. However, when the angle (xcex1) between the substrate and the inclined surface of the laminate is 60 degrees, the deposition angle (xcex8) must be 30 degrees or more in order to obtain a ratio b/a of 1 or more. In order for the ratio b/a to be reliably 1 or more, b/a must be in the range of 1 to approximately 1.75, and therefore, the deposition angle is more preferably set in the range from 19 to 48 degrees assuming that the angle (xcex1) between the substrate and the inclined surface of the laminate is 20 to 45 degrees.
The substrate provided with the bias underlying layers with predetermined thicknesses is subjected to sputtering again to form the bias layers and the conductive layers, and thus the spin-valve thin-film magnetic element is completed. At this stage, the sputtering targets may be disposed parallel to the substrate.
By constructing a magnetic head using the spin-valve thin-film magnetic element thus obtained, the magnetic head can exhibit high performance even if the track width is narrowed in order to cope with a higher recording density.